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Levothyroxine

SynthroidThyroid hormoneOral tablets, capsules, solution, and injectable forms

Mechanism

Provides synthetic thyroxine, which is converted to triiodothyronine and regulates metabolism, growth, and development.

Uses

  • Hypothyroidism replacement therapy
  • Pituitary thyrotropin suppression in selected thyroid conditions

Common effects

  • Symptoms of thyroid hormone excess
  • Palpitations
  • Tremor
  • Heat intolerance

Serious risks

  • Cardiac effects from overtreatment
  • Reduced bone mineral density with overreplacement
  • Not indicated for weight loss
  • Clinically important absorption interactions

Monitoring

  • TSH
  • Free thyroxine when appropriate
  • Symptoms and adherence
  • Changes in interacting medicines or products

Counseling

  • Take consistently on an empty stomach as directed
  • Separate from calcium, iron, and other binding products
  • Stay with a consistent product when possible
  • Report persistent symptoms of underreplacement or excess
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